Rotatably opening/closing doors have been widely used for buildings, furniture, ornaments and the like and many of the opening/closing structures of such doors have an opening/closing structure in which an axial member (convex portion) and a bearing (concave portion) are rotatably fixed in the concave-convex engagement. In Patent Document 1, the basic configuration of the door opening/closing structure also provides bearings in the center line of rotation at the door side and the main body side, which is an object to which the door is attached, and axial members rotatably engages in both bearings. However, these conventional door opening/closing structures are not intended for attachment/detachment of the door. Therefore, if the door is tried to be detached from the main body, it is not easy to attach and detach the door because of the interruption between the concavity and convexity of the axial members and the bearings.
Further, in Patent Document 2, the basic configuration is a concave-convex engagement fixation of a hinge axis (convex portion) and an engagement hole (concave portion), and there is proposed a hinge which is configured such that the hinge axis can be moved up and down and when the hinge axis comes close to the engagement hole, the hinge axis is protruded by the attraction of magnets provided in both of the hinge axis and the engagement hole, thereby the concave-convex engagement of the hinge axis and the engagement hole is achieved. However, this hinge is also included in a technique of fixing a door to an object to which the door is attached in the concave-convex engagement and if the door is tried to be detached from the main body, another means for releasing the concave-convex engagement fixation is required and thus the attachment/detachment of the door is not easy.